Mar resistant coatings are thin film coatings that resist smudging and scratching. These coatings typically have a textured or matt appearance. Mar resistant coatings find utility in many graphics applications, i.e. labeling and detailing. Additionally, mar resistant coatings are applied to wood surfaces to enhance abrasion and chemical resistance without compromising the quality of the underlying wood finish.
Such coatings have previously been formed from compositions of thermoplastic coating material such as thermoplastic, (meth)acrylic or (meth)acrylic-styrene copolymer emulsions. These compositions are applied to the substrate during wet-trap, off-line dry-trap, gravure, offset, silk-screen, flexography and related printing and coating processes. Once applied, the compositions provide superior film characteristics which include high gloss, mar resistance, oil resistance, and water resistance. These film characteristics are a function of composition weight and the percentage of solids in the composition. In general, high weight and high solid content correlate to superior film characteristics.
In order to achieve high weight and solid content, high quantities of volatile organic compounds (VOCs) are added to thermosetting compositions. These VOCs do not incorporate into the final coating after curing. Instead, the VOCs escape into the ambient. Once introduced into the environment, VOCs pose substantial hazards associated with inhalation. Such thermosetting solvent based systems are undesirable because of the hazards and expenses associated with VOCs.
UV curable compositions which do not contain VOCs are known in the art. UV compositions are cured through rapid photo-induced polymerizations instead of thermal energy which releases VOCs into the atmosphere. Since the UV curing process is essentially solvent free, the necessity for time consuming and expensive pollution abatement procedures is greatly reduced.
UV curable mar resistant coatings offer several other benefits not associated with thermally cured coatings. First, faster cure times offer substantial economic benefits. Furthermore, heat sensitive materials can be safely coated and cured with UV light without thermal degradation of the heat sensitive substrate. Additionally, UV light is a relatively low cost source of energy due to its widespread availability.
Although UV curable mar resistant coatings are superior to their thermal counterparts, there are still disadvantages inherent in UV curable coatings. Since UV curable mar resistant coatings require compositions which have high molecular weight and viscosity, it is difficult to apply the composition through spraying and brushing. Additionally, many UV curable mar resistant coatings require compositions that are prone to dispersion and instability. By using these compositions, the curing results in an uneven and blemished coating.
Accordingly, there exists a need to provide environmentally safe UV curable mar resistant coatings which exhibit an improved finish and resistance to smudging and scratching. Additionally, there is a need to provide a method of applying the coatings which furthers the goal of improved performance.